The present invention generally relates to liquid-to-air heat exchangers, and more particularly, to a method and apparatus of continually operating a heat exchanger prone to icing.
Liquid-to-air heat exchangers are used in various applications including for chilling passenger compartment air in aircraft. This type of heat exchanger works by exchanging thermal energy by thermal conduction. Air is directed across a surface having a large area cooled by a liquid. As the air flows across the surface the air near the surface begins to cool. If the temperature of the air drops to or below a dew point temperature of the air, water suspended within the gas begins to condense on the surface and form ice. This ice can block air flow through the passages, thereby reducing the overall efficiency of the heat exchanger. Conventionally, this problem is addressed by maintaining the liquid in the heat exchangers at a temperature above freezing for water or by periodically bypassing the chilled liquid to permit the air to warm the cooled exchanger surface and melt accumulated ice.
When the liquid temperature is maintained above freezing to prevent the condensate from freezing in the air passages, the cooling capacity of the heat exchanger is negatively impacted. Further, defrosting the entire heat exchanger at once interrupts cooling, which affects passenger comfort. In addition, the duration of the defrost cycle is a function of air temperature and humidity so additional sensors and sophisticated logic are required. Further, defrosting the entire heat exchanger dramatically increases the water flow into the air. The air flow and water flow need to be carefully managed so water is not entrained into the air and sprayed into the passenger compartment.
As will be appreciated by those skilled in the art, cooling capacity could be greatly increased if the exchanger could be defrosted without significantly impacting air delivery rates and liquid temperatures. Continual cooling would minimize performance impact